1. Field
The present disclosure relates to tomography apparatuses and methods of reconstructing tomography images.
2. Description of the Related Art
Medical imaging apparatuses are used to acquire images showing an internal structure of an object. The medical imaging apparatuses are non-invasive examination apparatuses that capture and process images of details of structures, tissue, fluid flow, etc., inside a body and provide the images to a user. A user, e.g., a medical practitioner, may use medical images output from the medical imaging apparatuses to diagnose a patient's condition and diseases.
A computed tomography (CT) apparatus is a representative example of an apparatus for imaging an object by emitting X-rays toward a patient.
A CT apparatus is capable of providing a cross-sectional image of an object and may represent an internal structure (e.g., organs such as a kidney, a lung, etc.) of the object without superimposition of adjacent structures, as compared to a general X-ray apparatus. Due to these advantages, the CT apparatus is widely used for precise diagnosis of diseases. A medical image obtained by a tomography apparatus is hereinafter referred to as a tomography image.
A tomography apparatus performs tomography scanning on an object to acquire raw data. The acquired raw data is used to reconstruct a tomography image. The raw data may be projection data obtained by projecting an X-ray onto the object, or may be a sinogram representing a set of projection data.
For example, to obtain a tomography image, image reconstruction may be performed using a sinogram obtained by performing tomography scanning. Tomography image reconstruction will now be described in detail with reference to FIGS. 1A and 1B.
FIGS. 1A and 1B are diagrams for explaining capturing and reconstruction of a CT image.
In detail, FIG. 1A is a diagram for explaining about a CT scan performed by a CT apparatus. During the CT scan, the CT apparatus acquires raw data while rotating around an object 25. FIG. 1B is a diagram for explaining about a sinogram acquired during a CT scan and a CT image reconstructed from the sinogram.
A CT apparatus generates and emits, via an X-ray generator, an X-ray towards an object, and detects, via an X-ray detector, the X-ray that has passed through the object. The X-ray detector may also generate raw data corresponding to the detected X-ray.
In detail, referring to FIG. 1A, an X-ray generator 20 in a CT apparatus emits an X-ray towards the object 25. During a CT scan performed by the CT apparatus, the X-ray generator 20 rotates around the object 25 and acquires a plurality of raw data 30 through 32 corresponding to angles of rotation of the X-ray generator 20. In detail, the X-ray generator 20 acquires the plurality of raw data 30 through 32 by detecting X-rays emitted toward the object 25 at positions P1 through P3, respectively. In this case, raw data may be projection data.
The X-ray generator 20 has to rotate 180 degrees or greater during a CT scan in order to produce a cross-sectional CT image.
Referring to FIG. 1B, a sinogram 40 may be acquired from a combination of the plurality of the raw data 30 through 32 acquired by the X-ray generator 20 that moves at predetermined angular intervals as described with reference to FIG. 1A. The sinogram 40 is acquired by performing a CT scan as the X-ray generator 20 rotates for one period. The sinogram 40 corresponding to the one period may be used to produce a cross-sectional CT image. The one period may be a time period for the X-ray generator 20 to rotate by an angle that is greater than or equal to 180 degrees or by an angle that is greater than or equal to 360 degrees depending on specifications for a CT system.
A CT image 50 is reconstructed by performing filtered backprojection (FBP) on the sinogram 40.
In general, it takes about 0.2 seconds for the X-ray generator 20 to rotate 180 degrees.
When an object to be scanned moves, motion of an object may occur even during one period. Due to the motion of the object, motion artifacts occur in a reconstructed CT image.
When motion artifacts occur, an outermost edge of an object may be unclear and may overlap with itself or others in a reconstructed CT image, and an inner edge of the object may be blurred within the CT image due to motion of the object.
These motion artifacts in a CT image may reduce the quality of the CT image and accordingly, degrade the accuracy of analysis of an image and diagnosis of a disease by a user, e.g., a medical practitioner.
Thus, when a CT scan is performed on a moving object, it is of great importance to reconstruct a CT image with minimized motion artifacts.